The invention relates to the field of disposable biomedical electrodes for establishing an electrical connection between the skin of the human anatomy and an electromedical apparatus. More specifically, the present invention relates to a disposable biomedical electrode used in conjunction with a reusable leadwire adapter for an electrocardiograph or similar monitoring equipment.
Medical electrodes of the foregoing type are utilized in a number of applications for a variety of purposes. The monitoring of physiological electric potentials to detect muscular activity of the heart muscle is generally well established, such apparatus being referred to in the art as electrocardiograph (also referred to herein as ECG) apparatus. The resulting traces derived from such apparatus provide a diagnostic tool for detecting heart disease and defects. Such monitoring of physiological electrical potentials may be employed in a number of other applications. However, the disposable biomedical electrode and reusable leadwire adapter of the present invention will be described herein with reference to their connection with ECG apparatus.
Such ECG traces may be desired in a number of different situations. For example, a simple ECG test to obtain a single tracing for diagnostic purposes may be carried out in a few minutes in a physician's office. Hence, medical electrodes utilized for such testing may be of a relatively simple disposable variety, since they are only in service for a very short time. Conversely, longer term monitoring applications require that the medical electrodes remain in place on the patient's skin for considerably extended periods of time. For example, in stress testing, the heart activity of the patient is monitored over a relatively longer period of time while the patient exercises on a tread mill or similar apparatus. Such testing may include monitoring of the heart activity during the exercise, as well as continued monitoring during the rest period thereafter so as to monitor the return of the heart to a normal or unstressed condition. Similarly, medical electrodes monitoring heart activity during surgery may be required to remain in place and operational for a period of several hours. In a similar fashion, patients hospitalized in an intensive care ward or other specialized care unit may require continuous, extended monitoring. Hence, medical electrodes utilized for long term ECG monitoring may be required to remain in service for many hours, and sometimes for many days.
Accordingly, there is a continuing need for high quality yet inexpensive medical electrodes for ECG and related uses which reliably transmit signals to enable traces to be obtained that accurately represent signals generated by the patient's heart. For purposes of convenience and safety, such medical electrodes should be inexpensive so that it is practical to dispose of them after only one use. In the past, an approach to providing inexpensive ECG medical electrodes has been to provide a disposable medical electrode which includes an electrolyte and a conductor engaged therein. For example, U.S. Pat. Nos. 4,773,424, 4,257,424, 4,643,193, 4,721,111 and 4,727,881 are all directed to disposable medical electrodes having an electrolyte and a conductor engaged therein.
It is generally recognized that, in order to obtain high quality traces, the portion of the electrode conductor engaged in the electrolyte should be a conductive material. A biomedical electrode may include a first electrical conductor that is galvanically inactive in the presence of the electrolyte and a second electrical conductor that is galvanically active in the presence of the electrolyte. The second electrical conductor may consist of a minute particle of conductive material located at the interface between the first electrical conductor and the electrolyte. The minute particle of conductive material at the interface can be practically any metal that is galvanically active in the presence of the electrolyte. The metals or metal compounds present at the interface are preferably substantially pure. For example, U.S. Pat. No. 3,976,055, herein incorporated by reference, teaches that the galvanically active material may consist of numerous different types of metals and may be applied to the first electrical conductor by varying methods and quantities.
It is preferable that the conductive material in a biomedical electrode consist of either silver or a silver coated conductive plastic. When pure metallic silver is used, the electrolyte will preferably contain a chloride ion, thus forming a conductor coating commonly referred to in the art as a silver/silver chloride system. Such silver/silver chloride systems provide a regular electrocardiograph traces having a stable base line. The silver/silver chloride system eliminates the erratic traces and wandering base lines sometimes attributed to defibrillation. However, the silver/silver chloride part of the electrode is extremely expensive when compared to the costs associated with the other components of the medical electrode. There have been many attempts in the past to minimize the expense associated with silver/silver chloride systems used in medical electrodes. For example, U.S. Patent No. 4,674,511 (commonly assigned) discloses a medical electrode for ECG monitoring which includes a conductor member comprising a thin strip of nonconductive material having a thin layer of electrically conductive paintable material adhered to one face thereof. By including only a thin strip of electrically conductive material on the medical electrode, the expense associated with such electrically conductive materials is minimized. However, the disposable medical electrode disclosed in U.S. Pat. No. 4,674,511 does in fact include the expensive electrically conductive material as a component and therefore, is discarded with the medical electrode. The disposition of the electrically conductive material increases the expense of using the disposable medical electrode.
As a response to such problems, attempts in the art have sought to provide a medical electrode having a reusable conductor portion. These medical electrodes typically comprise a disposable portion and a reusable conductor portion. For example, U.S. Pat. No. 4,653,501 (commonly assigned) discloses a medical electrode with a reusable conductor comprising a disposable electrode pad with a socket for receiving a reusable electrode conductor which is attached to a leadwire. The pad includes a socket plate having a release coated lower surface and a bore filled with a gel matrix which serves as the electrolyte contacting the patient's skin. In use, the medical electrode is applied to the skin of the patient and the releasable part of the clamp plates is peeled away from the socket plate. The electrode conductor is then inserted into the bore of the socket plate and the clamp is readhered to the socket plate in a covering relationship. The leadwire is then attached to the end such that the end of the leadwire and the electrode conductor are securely held in place relative to the electrolyte gel matrix.
Another attempt to minimize the expense of the medical electrode by incorporating a reusable conductor is disclosed in U.S. Pat. No. 4,635,642 (commonly assigned). The medical electrode comprises an electrode pad provided with a socket and a reusable electrode conductor which is attached to a leadwire. The electrode pad includes a laminated assembly of a pair of foamed sheets with an electrolyte gel matrix filling the gap between the foam sheets. An electrically nonconductive socket plate is disposed over the gel matrix and the foam sheets. The socket plate is provided with a socket or bore for receiving the reusable electrode conductor. The reusable electrode conductor has a ridged body slightly larger than the bore such that the bore resiliently engages the conductor. While these medical electrode assemblies may incorporate a reusable conductor, they are relatively expensive to manufacture in view of their complex structure as compared to other medical electrodes. Accordingly, medical electrodes having reusable conductors require a relatively sophisticated manufacturing scheme which significantly increases the cost of each medical electrode. Such costs substantially negate any savings associated with the reusable conductor feature.
Further, medical electrodes having reusable conductors in the prior art require non-standardized leadwires. Most hospitals and health care providers are equipped with standard leadwires which comprise a female portion of a snap fastener. The disposable electrode comprises the male portion of the snap fastener which snaps into the female portion of the standard leadwire. Non-standardized leadwires necessitate complete conversion within a hospital which is extremely difficult and expensive.
Accordingly, there remains a need in the art for a reusable leadwire adapter which is adaptable to standard leadwires; there is also a need for a disposable biomedical electrode assembly having a simple structure which is relatively inexpensive to manufacture; there is also a need for a biomedical electrode assembly which eliminates the expensive metallic conductive materials from the disposable portion of the biomedical electrode assembly so as to decrease the costs associated with use.